The Seattle Times reports that recent tests found a potential flaw and prompted the company to make a fundamental design change to the software.

Boeing is making changes to the 737 Max flight-control system’s software architecture after the FAA discovered potential issues during its June testing, according to a report.

The Seattle Times reports the FAA rejected Boeing’s assumption that pilots can serve as the “backstop safeguard” in emergency situations, including such as uninstructed movement of the horizontal tail. The FAA ruled that out in June, the report said, when while testing of the effect of a computer hardware glitch, one in three pilots in a simulation could not save the plane.

The FAA also identified a possible glitch with the flight-control computer’s microprocessor, the report said.

In response to the identified glitch, the Times reports Boeing plans to change the Max flight-control system’s software architecture. The change will allow the aircraft’s system to take input from both flight-control computers. In the past, the aircraft relied on only one computer during the flight.

"This is a huge deal," Peter Lemme, a former flight-controls engineer at Boeing, told the publication.

Lemme said the planned software change will resolve the microprocessor glitch and increase the reliability and safety of the Maneuvering Characteristics Augmentation System, which malfunctioned on both of the crash flights.

Boeing plans to have its new software architecture ready for testing by the end of September, according to the report.